There are many types of limited use or disposable protective apparel that are designed to provide barrier properties. Examples of such apparel include surgical gowns, patient drapes, face masks, shoe covers, industrial work wear and coveralls. Other examples include outer covers of disposable personal care products such as disposable diapers and incontinence garments.
For most applications, protective apparel needs to be made from fabrics that are relatively impervious to liquids and/or particulates. These barrier fabrics must also be suited for the manufacture of protective apparel at such low cost that the garments may be discarded after only a single use. Most inexpensive materials used for protective apparel have an important flaw. They are uncomfortable.
One such barrier fabric is a calendered flash-spun polyethylene spunbond fabric known as Tyvek.RTM.. This fabric is available from E. I. duPont De Nemours & Company. Although Tyvek.RTM. is inexpensive, it offers little breathability or stretch and so is uncomfortable to wear. Another type of material is generally known as spunlace fabric. E. I. DuPont De Nemours & Company provides a spunlace fabric under the trade designation Sontara.RTM.. Spunlace fabric generally refers to a material which has been subjected to hydraulic entangling. Although spunlace fabric is relatively inexpensive, breathable and can be deformed, the deformation is generally considered to be permanent and can be described as non-recoverable stretch.
Nonwoven webs of very small diameter fibers or microfibers have long been known to be permeable to air and water vapor while remaining relatively impermeable to liquids and/or particulates. Useful webs of small diameter fibers can be made by extruding non-elastomeric thermoplastic polymers utilizing fiber forming processes such as, for example, meltblowing processes. Although nonwoven webs of meltblown fibers formed from non-elastomeric polymers are relatively inexpensive and breathable, those highly entangled webs tend to respond poorly to stretching forces. Elongation that occurs in such materials is generally considered to be a permanent, non-recoverable elongation (i.e., non-recoverable stretch). For example, nonwoven webs made from conventional thermoplastic polypropylene are usually considered to have non-recoverable stretch.
It is desirable to have a material that is permeable to air and water vapor yet is relatively impermeable to liquids and/or particulates. Such a "breathable" material can dramatically increase the comfort of someone wearing a garment, especially if the garment must be worn under high heat index conditions, during vigorous physical activity, or for very long periods. Ventilation holes, ports and/or panels may be relatively ineffective and can compromise the protection of the wearer. Furthermore, a process of manufacturing garments with ventilation holes, ports and/or panels generally tends to be more complex and less efficient than a process of making garments without such features. Complex and relatively inefficient manufacturing processes can eliminate the cost advantages provided by inexpensive materials.
With respect to stretch properties, materials which are readily stretchable and have recovery (i.e., materials that contract upon termination of a biasing force following stretching of the material by application of the biasing force) are generally considered to be more comfortable than materials having "non-recoverable stretch" (i.e., materials that do not contract upon termination of a biasing force). Stretch and recovery is desirable in situations where sudden movement could cause a garment made of an unyielding fabric to rip open. Also, stretch and recovery are desirable in situations where sagging fabric or very loose fitting, baggy garments may snag and tear or otherwise pose a hazard.
In the past, stretch and recovery have been imparted to garments by adding elastomeric sections, pieces and/or strips. These elastomeric components have included nonwoven webs made from elastomeric polymers. Although such elastomeric materials provide highly desirable stretch and recovery, they are relatively expensive when compared to non-woven materials made from non-elastomeric polymers such as, commodity polyolefins. Additionally, some elastomeric materials may degrade upon exposure to certain liquids and/or gases that can be present in many industrial and medical environments. Furthermore, a process of manufacturing garments by joining several different types of fabric together generally tends to be more complex and less efficient than a process of making garments from a single fabric. Complex and relatively inefficient manufacturing processes generally reduce the cost advantages provided by inexpensive materials.
One material that has demonstrated stretch without requiring elastomeric materials has been suggested in U.S. Pat. No. 4,965,122. According to that patent, a tensioning force is applied to a fabric to reduce its width while the fabric is at ambient temperature. The material is then heated and cooled while it is necked so that it retains a memory of its necked condition which causes it to recover to generally about its necked dimensions after non-destructive stretching in the necked directed. While such a process works well with certain materials, it is largely unacceptable for treating a nonwoven web of very fine fibers such as meltblown microfibers, especially when it is important to preserve the barrier properties of the web. Generally speaking, nonwoven webs of non-elastic meltblown microfibers suitable as barrier materials have a highly entangled network of fibers. Instead of necking, such webs tend to tear or rip when any appreciable tensioning force is applied at room temperature.
Thus, a need exists for an inexpensive material which is permeable to air and water vapor yet relatively impermeable to liquids and/or particulates and which has stretch and recovery properties. There is also a need for a material having those properties which is relatively tough, durable, conformable, lightweight and suited for high-speed manufacturing and converting processes. There is a need for apparel/garments that are relatively impermeable to liquids and/or particulates and require little or no other materials, components, treatments, or the like to provide desirable comfort features such as, for example, conformability, breathability, and stretch and recovery properties. For example, a need exists for protective garments that are composed substantially or entirely of an inexpensive material such that the garments are relatively impermeable to liquids and/or particulates and so inexpensive as to be disposable while also being conformable, breathable, and having stretch and recovery properties.